PCB layout - JHarvey

[AbeFM]

The included pack is.... minimal. Even things like dual row headers of different lentghts are hard to find (though I did find a cable header that's right, I figure someone could make two "instant" configurations, one for testing one for running, just pull the plug.

I'd utterly forgotten that link you'd sent, which I shall be checking out directly.

[jharvey]

If we make a symbol or footprint, we probably want to consider sparkfun's tutorial. There was some good stuff about offsetting your line of holes to make for easier and better quality board assembly.

http://www.sparkfun.com/commerce/tutori ... als_id=114

also

http://www.sparkfun.com/commerce/tutori ... als_id=115

[AbeFM]

The first one, the offsets, while interesting, doesn't grab me - is that really true you need to make the pins bigger? That sounds like leftover from a round pin in a round hole. A square pin in a tight fitting hole should be good enough! Anyway, like he said I think it's more an issue with production line stuff - I just push it flat with my finger - something I'm holding on the pin I'm not soldering on, though the guy who mentioned using a breadboard in the comments seem to be onto something...

Nonetheless, I think I would try the smaller holes - you'd get a great fit, and wouldn't have enormous holes everywhere.


The second one is more general, lots of good info - I wonder how long it takes numbers (12 mils clearance) to be outdated? Then again, none of the rules looked hard to follow - noise rejection rings seem more of a problem to me.

Do we have a 2 layer board? I'd love to do four. Well, I'm torn - four is awesome for noise giving you a ground and power plane, but two is awesome cause you can drill it at will to make changes - something I always want to do on my MS but cannot.

Much of the tutorial is Ms specific. Perhaps when I finish this board for the MS adapter, I'll post it up here for critiquing, then when I send it off, we can look at the results and learn before printing FreeEMS boards.
-Abe.

[jharvey]

My understanding about why you leave the extra room around a PCB pin, if you don't the solder doesn't like to flow around the pin as nicely. The skin effect of the solder can stop it from flowing from one side of the PCB to the other side. So if you want to get nice rugged connection, you'd have to solder from both sides leaving a void in the middle of the PCB via. This void can cause a number of problems allowing a place for moisture to accumulate, varying your capacitance and creating a place for corrosion. I'm sure you can't wash the flux off from parts inside the board. However, I'd also agree, if I want the pins on my header to match the socket on the TA card, I'll put the headers on the TA card, then tack in a couple of the headers pins, then remove the TA card, then finish soldering the header. This will ensure it's aligned with the TA card, and compensation for any alignment variations that TA assembly house may have had.

My preference is two layer boards. Much easier to get a scope on parts when you can access them. I'm also not a fan of using flooded copper ground and power planes. The currents run wherever they feel, and often not in a straight line like you might thing. I feel that even though the noise floor is a bit lower, the coupled energy is a different story. You can avoid having the antennas coupling energy, if you run traces on your power planes, but then you're kind of missing the point of the 4 layer board. I feel the power planes is an easy of construction / ease of design thing, not so much an better end design thing. This is why I made my version with two, 2 layered boards. The power planes can be included in the connection board, for those that have an OEM connector to connect to.

About the noise floor thing, I've run a non current carrying ring around the outside edge of almost all of the board. This should help keep most stray RF energy from causing a noise floor issue. At this point RF noise should be higher than several hundred MHz. If we get coupling below several hundred MHz, it's most likely from the wires leaving the PCB, not the board layout.

[toalan]

Someone told me that the schematic and layout files are available, I thought they would be posted in this thread but I can not seem to find it. I just ordered a cnc machine, and I would be up for routing a few double sided boards for you guys.

Regards,

Alan To

[jharvey]

They can be found on the source forge download section. The layout is mostly done, but we are holding off on connecting the different circuits to the different CPU pins until, the software evolves some more. If you look at them, you'll see the tracks simply end a bit shy of the XOR chip. So they aren't ready to make yet, however, they are up for review. Feel free to comment on them, I'd be very happy to hear some more feed back about this layout.

For those that don't have or want to install KICAD, there is a PDF copy up there as well.

Also don't forget the wiki page. http://freeems.aaronb.info/wiki/doku.php?id=freeems_1.0

Enjoy.

[AbeFM]

Hmm, not sure about the "where the power goes" thing, you sure would think it would follow pretty close the trace above it. But it's a case of "if it works, I'm fine with it". And I can't pretend enough expertise to advise against the two layer board - if it were four, in my mind, it would be only ground planes.


The only actual exception I take to the board as laid out is (what I remember from discussion) avoiding vias. If you laid it out ok, and it doesn't take up too much space, fine. It's hard to imagine you could!

BTW, my copy of KiCAD on linux wanted to update itself, which I haven't yet done. Someone should bring up what's done now into the latest version make sure it saves and loads ok, works across windows and linux, etc.

"kicad - 2007.07.09-2.fc8.i386 updates kicad - 0.0.20080825c-2.i386"
I've been putting off updating, but I say we should find the latest version of KiCAD which is available on all reasonable platforms, and make sure our files work there. I had MAJOR problems when I had the PC on one version of the software and linux on another - moving files back and forth took a lot of text file editing.

Do you think you'd have time for that?

[jharvey]

Hmmm, perhaps I'm asking yum wrong, or perhaps my MythDora box doesn't use quite the same repository as yours. Looks like yours is Fedora Core 8 is that right? Here's a snap shot from my attempt to upgrade / update. Do you have a repository that isn't in my list of repositories?

# yum update kicad
Loading "kmdl" plugin
mythdora-updates 100% |=========================| 951 B 00:00
livna 100% |=========================| 2.1 kB 00:00
fedora 100% |=========================| 2.1 kB 00:00
atrpms 100% |=========================| 951 B 00:00
primary.xml.gz 100% |=========================| 201 kB 00:13
atrpms : ################################################## 818/818
mythdora 100% |=========================| 2.1 kB 00:00
updates 100% |=========================| 2.6 kB 00:00
Setting up Update Process
Could not find update match for kicad
No Packages marked for Update
# yum list installed | grep -i kicad
kicad.i386 2007.07.09-2.fc8 installed
# yum upgrade kicad
Loading "kmdl" plugin
Setting up Upgrade Process
Could not find update match for kicad
No Packages marked for Update

[Fred]

Debian unstable :

Code: Select all

fred@rwdlsd:/var/cache/apt/archives$ l kicad*
-rw-r--r-- 1 root root 2813202 2008-10-03 22:32 kicad_0.0.20080825c-1_i386.deb
-rw-r--r-- 1 root root 9385696 2008-10-03 22:32 kicad-common_0.0.20080825c-1_all

Code: Select all

fred@rwdlsd:~$ apt-get install kicad
Reading package lists... Done
Building dependency tree       
Reading state information... Done
kicad is already the newest version.

You don't get much fresher than that without going from source.

Fred.

[AbeFM]

http://kicad.sourceforge.net/wiki/index.php/Main_Page

Download
KiCad current release: 20080825


KiCad test versions from SVN:

Warning These versions are for developers and testers only!

* for Windows: 20080906-r1238-win32

* for Linux: 20080320-r918-linux or beischer.com/kicad

* for Mac (Universal): kicad_osx_v1345

* sources: 20080804-r1176-src or beischer.com/kicad

0805 seems the one to use. Want to make the switch?